1. Field of the Invention
This invention is related to piezoresistive sensors for micro-electro-mechanical systems (MEMS) and nano-electro-mechanical systems (NEMS).
2. Description of the Prior Art
Piezoresitive displacement detection techniques are attractive in both microelectromechanical and nanoelectromechanical systems (MEMS and NEMS), because they can be fully integrated and are easy to use. Applications include scanning probe microscopy, force and pressure sensors, flow sensors, chemical and biological sensors, and inertial sensors such as accelerometers and motion transducers. Most of these applications use p-type doped silicon layer as the sensing element. Doped silicon has a fairly high gauge factor (20˜100), but also high sheet resistance (10 kOhm/square) and therefore a relatively large thermal noise floor. Much higher 1/f noise is also expected in doped silicon due to its low carrier density. Additionally, fabrication processes for semiconducting piezoresistors, such as ion implantation or molecular beam epitaxy, are complicated and expensive. Finally, semiconducting materials are also vulnerable to processing damage. Therefore, they are not suitable for some uses at nanoscale dimensions.
There is an unmet need for a piezoresitive sensing element for microelectromechanical and nanoelectromechanical systems that is more sensitive and easier and cheaper to fabricate.